Immunotoxicity of silicon dioxide nanoparticles with different sizes and electrostatic charge

Silicon dioxide (SiO(2)) nanoparticles (NPs) have been widely used in the biomedical field, such as in drug delivery and gene therapy. However, little is known about the biological effects and potential hazards of SiO(2). Herein, the colloidal SiO(2) NPs with two different sizes (20 nm and 100 nm) and different charges (L-arginine modified: SiO(2)(EN20[R]), SiO(2)(EN100[R]); and negative: SiO(2)(EN20[−]), SiO(2)(EN100[−]) were orally administered (750 mg/kg/day) in female C57BL/6 mice for 14 days. Assessments of immunotoxicity include hematology profiling, reactive oxygen species generation and their antioxidant effect, stimulation assays for B- and T-lymphocytes, the activity of natural killer (NK) cells, and cytokine profiling. In vitro toxicity was also investigated in the RAW 264.7 cell line. When the cellularity of mouse spleen was evaluated, there was an overall decrease in the proliferation of B- and T-cells for all the groups fed with SiO(2) NPs. Specifically, the SiO(2)(EN20(−)) NPs showed the most pronounced reduction. In addition, the nitric oxide production and NK cell activity in SiO(2) NP-fed mice were significantly suppressed. Moreover, there was a decrease in the serum concentration of inflammatory cytokines such as interleukin (IL)-1β, IL-12 (p70), IL-6, tumor necrosis factor-α, and interferon-γ. To elucidate the cytotoxicity mechanism of SiO(2) in vivo, an in vitro study using the RAW 264.7 cell line was performed. Both the size and charge of SiO(2) using murine macrophage RAW 264.7 cells decreased cell viability dose-dependently. Collectively, our data indicate that different sized and charged SiO(2) NPs would cause differential immunotoxicity. Interestingly, the small-sized and negatively charged SiO(2) NPs showed the most potent in vivo immunotoxicity by way of suppressing the proliferation of lymphocytes, depressing the killing activity of NK cells, and decreasing proinflammatory cytokine production, thus leading to immunosuppression.